Rotating injectors are widely used in industry for the purpose of floating separation of impurities in molten metal, by blowing a dispersion of an inert gas, such argon, nitrogen, chlorine, and the like into the melt.
Prior art rotating injectors normally comprise a hollow rotary shaft and a rotating mixer made of sintered carbon or ceramic material. The inert gas is flowed out of holes having a diameter greater then 1 mm, located at the downward end or on the side of the rotating mixer, which rotates at high speed.
Because of the size of the holes, in excess of 1 mm in diameter, the diameter of the inert gas flow through the holes when the rotating injector is not being rotated may exceed 5 mm.
To effect efficient removal from the molten metal, it is important that the area of contact between the inert gas and the molten metal be as large as possible, and thus the rotating injector has been rotated at a higher speed (200-800 rpm) to enable micronization and dispersion of the gas over the entire vessel.
From a macro standpoint, the micronization of the inert gas by means of higher speed rotation of the mixer is effective. However, the inert gas is thereby caused to be `sticky`, and its expansion in volume tends to lower the area of contact with the molten metal due to the agitation, during floating of the inert gas once micronized, as it is dispersed upwards to the molten metal surface.
In addition, due to the higher agitation force of the rotating injector, eddy currents or ripples are produced on the molten metal surface during the agitation, oxides are formed on contact with atmosphere, and hydrogen is absorbed into the molten metal. All of these phenomena have long been regarded as serious problems.